1. Field of the Invention
The present invention relates to a metal diaphragm type pulsation absorber for a high-pressure fuel pump.
2. Description of the Prior Art
A diesel engine is widely known as an engine in which fuel is injected in the cylinders of the engine, so-called "intra-cylinder injection engine" or "direct injection engine". An intra-cylinder injection system has recently been proposed for a spark-ignition engine (gasoline engine). This intra-cylinder injection engine is constituted to obtain a sufficiently high fuel injection pressure and required to suppress fuel pressure pulsation for stable injection. Therefore, a compact, single-cylinder high-pressure fuel pump which has a simple structure and is produced at a low cost is already known. Since the single-cylinder high-pressure fuel pump has only one plunger, the pressure of fuel to be injected has a considerable pulsation width. Therefore, a metal bellows type or metal diaphragm type pulsation absorber for absorbing this pulsation is proposed for the single-cylinder high-pressure fuel pump.
FIG. 8 is a diagram typically showing an auto fuel supply system of the prior art. In FIG. 8, reference numeral 1 denotes a delivery pipe which is a fuel injector, and 2 the injectors of the delivery pipe 1 corresponding to the number of unshown engine cylinders. Denoted by 3 is a high-pressure fuel pump installed in a housing, and 4 the high-pressure pump of this high-pressure fuel pump 3. This high-pressure pump 4 is an element for increasing the pressure of fuel to a high level by means of a piston driven by an unshown cam which rotates at a rotation speed half that of an engine and a cylinder for containing this piston in such a manner that it can reciprocate. Reference numeral 5 represents a low-pressure passage connected to the inlet port of the high-pressure pump 4, 6 a filter installed in the low-pressure passage 5, 7 a metal bellows type low-pressure damper connected to the low-pressure passage 5 between the high-pressure pump 4 and the filter 6, 9 a high-pressure passage connected to the outlet port of the high-pressure pump 4, 10 a diaphragm type high-pressure damper connected to the high-pressure passage 9 by a branch passage 11, 12 a high-pressure check valve installed in the high-pressure passage 9 on the outlet side of the high-pressure damper 10, 13 a high-pressure back passage which branches off from the high-pressure passage 9 on the outlet side of the high-pressure check valve 12, 14 a filter installed in the high-pressure back passage 13, 15 a high-pressure regulator installed in the high-pressure return passage 13 on the downstream side of the filter 14, 16 the drain passage of the high-pressure pump 4, 17 a high-pressure pipe for connecting the high-pressure passage 9 of the high-pressure fuel pump 3 to the delivery pipe 1, 18 a fuel tank, 19 a low-pressure pump installed in the fuel tank 18, 20 a filter on the inlet side of the low-pressure pump 19, 21 a low-pressure pipe for connecting the outlet side of the low-pressure pump 19 to the inlet side of the high-pressure fuel pump 3, 22 a low-pressure check valve installed in the low-pressure pipe 21, 23 a filter installed in the low-pressure pipe 21 closer to the high-pressure fuel pump 3 than to the low-pressure check valve 22, 24 a low-pressure back pipe for connecting the high-pressure fuel pump 3 side and not the filter 23 side of the low-pressure pipe 21 to the fuel tank 18, 25 a low-pressure regulator installed in the low-pressure back pipe 24, 26 a drain pipe for connecting the drain passage 16 of the high-pressure fuel pump 3 to the fuel tank 18, 27 a high-pressure back pipe for connecting the high-pressure back passage 13 of the high-pressure fuel pump 3 to the fuel tank 18, and 28 fuel stored in the fuel tank 18.
A description is subsequently given of the operation of the above fuel supply system. The low-pressure pump 19 sucks the fuel 28 through the filter 20, increases the pressure of the fuel 28 to a low level and discharges it. This low-pressure fuel 28 is supplied to the high-pressure fuel pump 3 by the low-pressure pipe 21 through the low-pressure check valve 22 and the filter 23. When the pressure of the fuel 28 in the low-pressure pipe 21 exceeds a low level set by the low-pressure regulator 25, part of the fuel 28 in the low-pressure pipe 21 is returned to the fuel tank 18 by the low-pressure back pipe 24 through the low-pressure regulator 25, thereby controlling the pressure of the fuel 28 to be supplied to the high-pressure fuel pump 3 from the fuel tank 18 to a predetermined low level. The fuel 28 which reaches the high-pressure fuel pump 3 is sucked into the high-pressure pump 4 through the filter 6 and the low-pressure damper 7 in the low-pressure passage 5. The high-pressure pump 4 increases the pressure of the sucked fuel 28 to a high level, discharges the fuel 28 in the high-pressure passage 9 and also drains the fuel 28 leaked between the piston and the cylinder of the high-pressure pump 4 in the drain passage 16. The fuel 28 drained in the drain passage 16 returns to the fuel tank 18 through the drain pipe 26. The fuel 28 supplied to the high-pressure passage 9 is delivered to the delivery pipe 1 through the high-pressure damper 10 and the high-pressure check valve 12. When the pressure of the fuel 28 in the high-pressure passage 9 exceeds a predetermined high level set by the high-pressure regulator 15, part of the fuel 28 in the high-pressure passage 9 is returned to the fuel tank 18 by the high-pressure back passage 13 and the high-pressure back pipe 27 through the filter 14 and the high-pressure regulator 15, thereby controlling the pressure of the fuel to be supplied to the delivery pipe 1 from the high-pressure fuel pump 3 to a predetermined high level. In this state, the high-pressure fuel 28 is injected into a cylinder at a fuel injection time by the injector 2 of the delivery pipe 1 corresponding to the fuel injection time for the cylinder of the engine.
FIG. 9 is a sectional view of the high-pressure damper 10 and a portion therearound of the high-pressure fuel pump 3. In FIG. 9, the high-pressure damper 10 is stored in a storage recessed portion 31 formed in the body 30 of the high-pressure fuel pump 3 and constitutes a high-pressure damper which is a fuel pulsation absorber. Reference numeral 100 denotes a case, one portion of a high-pressure container, and 101 a plate as the other portion of the high-pressure container which is stored in the bottom of the storage recessed portion 31 of the body 30. Denoted by 102 is a flexible thin metal disk-like diaphragm which forms a first high-pressure chamber 103 with the case 100 and a second high-pressure chamber 104 with the plate 101. A peripheral portion of the diaphragm 102 is sealed by and supported between the case 100 and the plate 101. Reference numeral 105 is an annular clamp screw which is mated with a threaded portion 32 of the body 30 to press fit the case 100, the diaphragm 102 and the plate 101 into the bottom of the storage recessed portion 31. A sealing material 33 such as an O ring is inserted between the outer peripheral wall of the plate 101 and the inner peripheral wall of the storage recessed portion 31 to prevent fuel leakage. First and second passage portions 34 and 35 constituting the branch passage 11 are formed in the body 30 in such a manner that they communicate with the bottom of the storage recessed portion 31. A dish-like first high-pressure chamber side stopper which is depressed upward and limits the movement of the diaphragm 102 is formed on the under surface (on the diaphragm 102 side) of the case 100. A recessed portion 107 which communicates with the first and second passage portions 34 and 35 is formed on the under surface (on the first and second passage portions 34 and 35 side) of the plate 101, a dish-like second high-pressure chamber side stopper 108 which is depressed downward and limits the movement of the diaphragm 102 is formed on the top surface (on the diaphragm 102 side) of the plate 101, and a plurality of through holes 109 which are open to the recessed portion 107 and the second high-pressure chamber side stopper 108 are formed in the plate 101 between the recessed portion 107 and the second high-pressure side stopper 108. Unshown gas is charged into the first high-pressure chamber 103 through a gas charging port 110 formed in the case 100 at a predetermined pressure and sealed by a plug 111. The predetermined pressure is required to absorb the pulsation of the high-pressure fuel passing through the second passage portion 35 from the first passage portion 34 through the recessed portion 107. The second high-pressure chamber 104 is filled with part of the high-pressure fuel from the recessed portion 107 through the through holes 109. 105a denotes a tool hole for operating the clamp screw 105. 112 represents a welded portion for sealing and supporting the peripheral portion of the diaphragm 102 with the case 100 and the plate 101.
A description is subsequently given of the operation of the high-pressure damper 10. When the fuel supply system of FIG. 8 starts operation by driving the engine while the first high-pressure chamber 103 is filled with gas and the second high-pressure chamber 104 is filled with fuel, the high-pressure fuel discharged by the high-pressure pump 4 flows into the second passage portion 35 from the first passage portion 34 through the recessed portion 107 as shown by arrows. When pulsation occurs in this fuel, the diaphragm 102 is bent toward the case 100 or toward the plate 101 by the total of the pressure of gas in the first high-pressure chamber 103 and the spring force of the diaphragm 102 itself to absorb the pulsation of the fuel. When a driver turns off the key switch of an automobile and the engine stops, the flow of the fuel shown by the arrows stops and the pressure of the fuel in the second high-pressure chamber 104 drops. Thereby, the pressure of the gas in the first high-pressure chamber 103 becomes higher than the total of the pressure of the fuel in the second high-pressure chamber 104 and the spring force of the diaphragm 102 itself, whereby the diaphragm is bent and finally contacts the second high-pressure chamber side stopper 108. When the pressure of gas in the first high-pressure chamber 103 is reduced by the removal of gas from the first high-pressure chamber 103, or when the diaphragm 102 is greatly bent due to a sudden rise in the pulsation pressure of the fuel, the diaphragm 102 finally contacts the first high-pressure chamber side stopper 106.
Since the high-pressure damper 10 which is the metal diaphragm type pulsation absorber of the prior art is constituted as described above, the diaphragm 102 can move toward the first or second high-pressure chamber side stopper 106 or 108 with spacing therebetween during the operation of the high-pressure damper 10 and reduces the pulsation of the fuel more as the thickness decreases. When the fuel flows into the second passage portion 35 from the first passage portion 34 through the recessed portion 107, foreign matter such as metal powders contained in the fuel may enter the second high-pressure chamber 104 from the through holes 109. When the foreign matter enters the second high-pressure chamber 104, it accumulates in the second high-pressure chamber 104 by the flow of the fuel in the second high-pressure chamber 104 caused by the movement of the diaphragm 102. When the diaphragm 102 contacts the second high-pressure chamber side stopper 108 by the suspension of the high-pressure fuel pump 3, the foreign matter accumulated in the second high-pressure chamber 104 is sandwiched between the diaphragm 102 and the second high-pressure chamber side stopper 108, whereby the diaphragm 102 is deformed by the foreign matter. There is a possibility that high stress is locally generated in the deformed portion of the diaphragm 102 and the diaphragm 102 is broken by cracking.